1. Field of the Invention
The present invention relates to a method of transferring elements from an element formation substrate on which a plurality of elements such as electrical elements or optical elements to an element disposition substrate at different pitches, the element disposition substrate with which the method of transferring elements is implemented, a device which is manufactured by applying the method of transferring elements, and a method of manufacturing the same.
2. Description of the Related Art
Heretofore, all of signal transfer between semiconductor chips each typified by a Large Scale Integrated Circuit (LSI) has been carried out by using electrical signals through substrate wirings. However, a communication amount of data required between the semiconductor chips has remarkably increased along with the recent high performance promotion for Microprocessor Units (MPUs), and thus the speeding up of the signals, and the densifying of the signal wirings have been required. As a result, the various high-frequency problems have arisen. A delay of the signal caused by the resistance and capacitance of the wiring, mismatching between the impedances, an Electro-Magnetic Compatibility/Interference (EMC/EMI) such as generation of a noise or a cross-talk, or the like is given as typical one of those problems. Here, the EMC/EMI means the compatibility, for the electro-magnetic environment, which prevents an electronic apparatus from giving or receiving an electromagnetic wave interference.
In order to solve those problems, the optimization of the wiring disposition, the development of the new materials, and the like have been carried out. However, for the purpose of realizing the further high function promotion, there has arisen the necessity for reviewing the mounting construction itself based on the simple mounting of the semiconductor chips. In order to cope with this situation, micro-wiring connection due to Multi-Chip Module (MCM) promotion, or the like has been proposed. In this multi-chip module, highly-functional chips are mounted to a precise mounting substrate such as a ceramic substrate or a silicon substrate, and thus the micro-wiring connection which can not be obtained in the existing multilayer printed wiring board is realized. As a result, the pitch narrowing of the wiring becomes possible, and the communication amount of data can be increased by widening a bus width.
In addition, an optical transmission coupling technique (optical interconnection) based on an optical wiring attracts attention as a technique for basically realizing the speeding up and capacity increasing of the signal communication. This technique, for example, is described in non-patent literary document of “Optical Wiring Encounter,” NIKKEI ELECTRONICS, Dec. 3, 2001, pp. 122 to 125, FIGS. 4 to 7, and Yasuhiro Andoh, “Tendency of Optical Interconnection Technology and Next-Generation Device Mounting Technology,” NTT R&D, Vol. 48, No. 3, pp. 271 to 280 (1999). With this technique, an electrical signal is converted into an optical signal, thereby largely increasing a transmission speed itself between chips. In addition, the optical signal does not require the measures to cope with the electromagnetic noise and the cross-talk at all, and thus a relatively flexible wiring design becomes possible.
The optical wiring can be applied between the electronic apparatuses, between the boards within the electronic apparatuses, between the chips within the board, and the like, and thus can be applied to various kinds of portions. For example, in the case of short-distance transmission of a signal, for example, between chips, as shown in FIG. 4, an optical waveguide 101 is formed on a printed wiring board 100 having chips mounted thereto. Also, an emitted light (for example, a laser beam), obtained through signal modulation, from a light emitting element (for example, a vertical cavity surface emitting laser) 104 is taken in from an inlet side end portion 102 of the optical waveguide 101 to be guided to an outlet side end portion 103 through the optical waveguide 101. Also, the emitted light thus guided is made incident to a light receiving element (for example, a photodiode) 105 through the outlet side end portion 103. An optical transmission/communication system in which the optical waveguide 101 is used as the transmission path for the laser beam obtained through the signal modulation can be constructed in the manner as described above.
A section for carrying out alignment among optical components (such as a light emitting element, a light receiving element, an optical waveguide, an optical fiber, and a lens), and connecting thereto optical paths, thereby carrying out position-fixing is essential for an optical wiring system. In this connection, the relatively positional precision between the optical components has to be satisfactorily held so that a connection loss of a light transmitted between the optical components falls within a tolerance. Hereinafter, in this specification, when no distinction is made between the light emitting element and the light receiving element, the light emitting element and the light receiving element will be referred to as “the photoelectric elements” in some cases. In addition, a process for carrying out alignment among the optical components, and connecting thereto the optical paths, thereby carrying out the position-fixing will be expressed hereinafter as the wording “the optical coupling is formed among the optical components.”
Hereinafter, an active alignment method of carrying out alignment while an intensity of a signal light is actually observed, a method of carrying out alignment while an alignment marker formed on a substrate or the like is observed by using a microscope or the like is known as an alignment method. However, a lot of trouble is taken with such an alignment method, and thus is one of the causes by which the optical wiring system is made expensive. Therefore, there is desired a method of carrying out alignment with excellent productivity and at a low cost in accordance with a self-alignment method, based on an outer shape, such as fitting (mating) or abutment.
In addition, some sort of positional reference may be required for carrying out the alignment. For example, in the case of the surface mounting system previously described with reference to FIG. 4, the mounting board such as the printed wiring board 100 is used as the positional reference. However, for the purpose of realizing a desired positional precision with the mounting board as the positional reference, highly precision increasing may be required for the mounting board itself, which causes high costs. In addition, even when the mounting board which is not essentially designed in order to meet such a purpose is desired to be used as the positional reference, the possibility that a predetermined performance may not be realized owing to thermal expansion or the like is high.
In order to cope with such a situation, the inventor of the present invention earnestly carried out the study repeatedly, and as a result, proposed a technique that a socket is used instead of using a mounting board, an optical information processor having an optical waveguide array built between a set of sockets is formed, thereby constructing an optical wiring system. This technique is described in Japanese Patent Laid-Open No. 2005-181610 (refer to pages 8, 10 and 11, and FIGS. 1, 5 and 17) referred to as Patent Document 1 hereinafter. This socket is formed in such a way that a socket in an IC package such as a Pin Grid Array (PGA) package or a Land Grid Array (LGA) package is used as a base, and four recess portions serving as an optical waveguide array installing portion are provided in the shape of a cross. Also, this socket has a positioning section for positioning the optical waveguide array.
FIG. 5A is a schematic perspective view when a socket 110 is viewed from a side of a surface on which an optical waveguide is installed, and FIG. 5B is a schematic perspective view when the socket 110 is viewed from the side opposite to the side of the surface on which the optical waveguide is installed. In the socket 110, each of a recess portion 112 and a protrusion portion 113 for positioning and fixing an optical waveguide array (not shown) is provided in four portions. The optical waveguide array is fitted to one recess portion 112 to carry out the positioning thereof in a width direction, and is also made to abut against the protrusion portions 113 to carry out the positioning thereof in a length direction. It is noted that a depth of the recess portion 112 is larger than a thickness of the optical waveguide array 111. Each of convex surfaces 114 of the socket 110 is provided with a conduction section for making conduction between a front surface and a back surface of the socket 110, for example, recess portions 115 of terminal pins.
FIG. 6A is a schematic cross sectional view showing a state in which constituent elements of an optical information processor using the socket 110 shown in FIGS. 5A and 5B is exploded, and FIG. 6B is a schematic cross sectional view showing a state in which the constituent elements are assembled into the optical information processor using the socket 110 shown in FIGS. 5A and 5B. This optical information processor is composed of a set of sockets 110-1 and 110-2 fixed onto a printed wiring board 130, an optical waveguide array 111 built between these sockets 110-1 and 110-2, and interposers 120-1 and 120-2.
As shown in FIG. 6A, semiconductor integrated circuit chips 124 and 125 are mounted on upper surface sides of the interposers 120-1 and 120-2, respectively. Also, light emitting element arrays 122 for emitting lights to the optical waveguide array 111, and/or light receiving element arrays 123 for receiving an incident light emitted from the optical waveguide array 111 are flip chip-mounted on lower surface sides of the interposer 120-1 and 120-2. Also, rewiring electrodes 121 are provided in peripheral portions of the interposer 120-1 and 120-2.
In fixing the interposers 120-1 and 120-2 to the sockets 110-1 and 110-2, respectively, as shown in FIG. 10B, the rewiring electrodes 121 are inserted into the recess portions 115 of the terminal pins of the sockets 110-1 and 110-2, respectively, thereby causing lower surfaces of the rewiring electrodes 111 to come in contact with the convex surfaces 114 of the sockets 110-1 and 110-2, respectively. As a result, the interposers 120-1 and 120-2 are positioned in the sockets 100-1 and 100-2, respectively, by the fitting of the rewiring electrodes 121 to the recess portions 115 of the terminal pins, and the abutment of the lower surfaces of the interposers 120-1 and 120-2 against the convex surfaces 114 of the sockets 100-1 and 100-2.
As with this prior example, the optical waveguide array 111, and the light emitting elements 122 and/or the light receiving elements 123 are aligned with each other through the sockets 100-1 and 100-2, and the interposers 120-1 and 120-2. For this reason, the precision of the optical coupling between the optical waveguide array 111, and the light emitting elements 122 and/or the light receiving elements 123 depends only on the manufacture precision of the sockets 100-1 and 100-2, and the interposers 120-1 and 120-2, and thus is independent of the manufacture precision of the mounting board such as the printed wiring board 130.
Moreover, the inventor of the present invention proposed a photoelectric converter which has a positioning section not depending on the manufacture precisions of the sockets and the interposers, and in which highly precise optical coupling can be formed at a low cost. This photoelectric converter is described in Japanese Patent Laid-Open No. 2006-258835 (refer to pages 8 and 9, and FIG. 1) referred to as Patent Document 2 hereinafter. FIG. 7A is a top plan view of a lower surface side (a light emission or light incidence side) of the photoelectric converter 210, FIG. 7B is a cross sectional view of the photoelectric converter 210 taken on line 7B-7B of FIG. 11A, and FIG. 7C is a cross sectional view of an optical waveguide module using the photoelectric converter 210 taken on line 7B-7B of FIG. 7A. In addition, dotted lines in FIGS. 7B and 7C indicate important members located in positions which are out of the cross sectional positions, respectively (and so forth on).
As shown in FIGS. 7A and 7B, in the photoelectric converter 210, a plurality of photoelectric elements 205 are disposed in an element mounting substrate 211. Although the three photoelectric elements 205 are shown in FIGS. 7B and 7C for the sake of convenience of illustration, the number of photoelectric elements 205 is especially by no means limited.
The photoelectric element 205 is either a light emitting element such as a Vertical Cavity Surface Emitting Laser (VCSEL), or a light receiving element such as a photodiode. The photoelectric element 205 is flip chip-connected in its electrode 206 formed on its upper surface to an interposer (not shown) or the like through a solder bump or the like to be electrically connected to a controlling semiconductor chip (not shown) or the like mounted to the interposer or the like. The semiconductor chip, for example, is a wafer-level Chip Scale Package (CSP).
A lower surface of the photoelectric element 205 is formed as either a light emission surface or a light incidence surface, and also an electrode is formed so as not to impede on optical path. A base glass 212 for strength reinforcement is joined to the optically-transparent electrode, and a glass substrate 213 is joined to the base glass 212 for strength reinforcement. The base glass 212 for strength reinforcement serves to hold the mechanical strength, and thus may be omitted (refer to Japanese Patent Laid-Open No. 2006-237428). Lens portions 214 are provided on the glass substrate 213. The lens portion 214 serves to collimate an emitted light, thereby preventing the emitted light from diffusing when the photoelectric element 205 is formed as the light emitting element. On the other hand, the lens portion 214 serves to condense an incident light on the light receiving element when the photoelectric element 205 is formed as the light receiving element.
As shown in FIG. 7C, the photoelectric converter 210 and an optical waveguide array 220 are combined with each other, thereby forming the optical waveguide module 230. In this case, the optical waveguide array 220 either guides a light emitted from the photoelectric converter 210 to the outside, or guides an incident light from the outside to the photoelectric converter 210. The optical waveguide module 230 is a unit module of an optical information processor which can be constructed by combining the two optical waveguide modules 230, that is, the optical waveguide module 230 on a side of transmission of an optical signal, and the optical waveguide module 230 on a side of reception of an optical signal with each other.
Each of optical waveguides of the optical waveguide array 220 is composed of a core 221 as a waveguide path, an upper cladding 222, and a lower cladding 223. An end surface of the core 221 is formed as a reflecting surface 224, having an inclination angle of 45°, for incidence/emission of a light to/from the photoelectric element 205. The upper cladding 222 in the vicinity of the end surface 224 is provided with a lens portion 225. When the photoelectric element 205 is formed as the light emitting element, the lens portion 225 serves to condense the emitted light from the light emitting element on the reflecting surface 224 having the inclination angle of 45° to guide the emitted light to the inside of the core 221. On the other hand, when the photoelectric element 205 is formed as the light receiving element, the lens portion 225 serves to collimate an incident light made incident from the outside to the core 221 to be propagated through the inside of the core 221 to be reflected by the reflecting surface 224 having the inclination angle of 45°. Thus, the lens portion 225 serves to prevent the incident light from diffusing, thereby sending the incident light to the photoelectric element 205.
The glass substrate 213 is provided with convex portions (pins) 231 each serving as a positioning section, and the upper cladding 222 of the optical waveguide array 220 is provided with recess portions 232 to which the convex portions (pins) 23 are intended to be fitted, respectively. The photoelectric element 205 of the photoelectric converter 210, and the core 221 of the optical waveguide array 220 are aligned with each other by the fitting of the convex portions (pins) 231 to the recess portions 232 to be optically coupled to each other. At this time, it is better that the photoelectric element 205 and the reflecting surface 224 having the inclination angle of 45° face each other with their optical axes being made to agree with each other, and the centers of the lens portion 214 and the lens portion 225 are located on an optical axis connecting the photoelectric lens 205 with the reflecting surface 224 having the inclination angle of 45°. By adopting this construction, when the photoelectric element 205 is formed as the light emitting element, the emitted light from the light emitting element, for example, is collimated into a parallel beam by the lens portion 214 to be sent out. Also, the resulting parallel beam is condensed on the reflecting surface 224 having the inclination angle of 45° of the optical waveguide array 220 to be efficiently guided to the core 221 of the optical waveguide array 220. On the other hand, when the photoelectric element 205 is formed as the light receiving element, the incident light which is made incident from the outside to the core 221 to be propagated through the outside of the core 221, thereby being reflected by the reflecting surface 224 having the inclination angle of 45°, for example, is collimated into a parallel beam by the lens portion 225 to be sent to the photoelectric element 205 side. Also, the resulting parallel beam is efficiently condensed on the light receiving surface of the photoelectric element 205 by the lens portion 214.
Therefore, when the convex portions (pins) 231 each serving as the positioning section, the recess portions 232 to which the convex portions 231 are fitted, respectively, and the lens portions 214 and 225 are manufactured with predetermined precisions, respectively, the optical coupling between the photoelectric element 205 and the optical waveguide core 221 can be formed with a desired precision. In such a manner, since the members associated with the optical coupling are miniaturized, the precision of the optical coupling is enhanced, and the cost lowering becomes possible. In addition, even an expensive material such as a material having a low coefficient of thermal expansion or a material having excellent processing characteristics can be used as long as the material has the excellent material characteristics. As a result, the precision can be further enhanced.
Now, there are many examples in each of which when the semiconductor device is manufactured using the semiconductor chips as with the photoelectric converter described above, wirings or the like for the power source are formed and the desirable semiconductor device is manufactured after a large number of semiconductor chips collectively formed on the element formation substrate are partitioned into pieces and the resulting pieces are rearranged at a desired pitch on the element mounting substrate.
For example, an image display device using light emitting diodes (LEDs) as display elements is one of those examples. In this case, the element formation substrate is diced to be partitioned into the LED chips, forming the respective pixels, which are taken out in turn. Also, the resulting LED chips are individually connected to the external electrodes through either the wire bonding connection or the bump connection based on flip chip. Normally, the pitch of disposition of the LED chips in the image display device is much larger than that of the LED chips on the element formation substrate.
In general, in the element formation substrate, it is desirable that for the purpose of effectively utilizing the expensive substrate, and enhancing the productivity, a large number of elements are formed at a pitch nearly equal to a size of the element as tightly as possible. On the other hand, in the element mounting substrate, the pitch between each adjacent two elements is determined to be a size most suitable for the utilization desire of the chips. Essentially, those two pitches are independent of each other. Thus, when after the individual elements are obtained through the partitioning, the elements are disposed at the predetermined pitch on the element mounting substrate one by one as with the existing case, a difference between the two pitches does not matter.
However, as the number of semiconductor chips increases, such a disposition process is laborious and thus becomes the expensive process. In addition, as the size of the semiconductor chip becomes small, it becomes difficult to handle the semiconductor chip after completion of the partitioning. Even so, when a plurality of elements formed on the element formation substrate are desired to be collectively handled without carrying out the partitioning, it is necessary to form the semiconductor chips on the element formation substrate at the same pitch as that in the element mounting substrate. This is not allowed for the enhancement of the productivity as well as for the effective utilization of the expensive element formation substrate.
In order to cope with such a situation, a thinning-out transfer method is known as follows. That is to say, although a plurality of elements formed on an element formation substrate are partitioned into pieces, the plurality of elements are not perfectly dissected out, but are collectively held on a temporary holding substrate while a pitch in the element formation substrate in the phase of manufacture is held. After that, a group of elements on the temporary holding substrate is thinned out and selected so that a pitch between each adjacent two semiconductor chips becomes a predetermined pitch. Also, the elements thus selected are collectively transferred from the temporary holding substrate to an element disposition substrate.
FIGS. 8A to 8D are respectively cross sectional views showing a flow of the thinning-out transfer method described in Japanese Patent Laid-Open No. 2002-198569 (refer to pages 4 and 5, and FIGS. 1 and 2) referred to as Patent Document 3 hereinafter. Hereinafter, an essential point of the thinning-out transfer method will be described with reference to FIGS. 8A to 8D.
In this thinning-out transfer method, firstly, as shown in FIG. 8A, a plurality of elements 305 formed on an element formation substrate are collectively held on a temporary holding substrate 321. An adhesive agent layer (not shown) or the like is formed on a surface of the temporary holding substrate 321, and can hold the elements 305 with its adhesive force. Although the elements 305 are partitioned into pieces, a pitch between each adjacent two elements 305 is the same as that in the element formation substrate. Moreover, an ultraviolet curable resin 308 is disposed on a surface of each of the elements 305.
Next, as shown in FIG. 8B, the elements 305 held on the temporary holding substrate 321, and the element disposition substrate 331 are attached firmly to each other in a state in which the ultraviolet curable resin 308 is uncured. A mask layer 332 having opening portions in element mounting positions, respectively, is disposed on a back surface of the element disposition substrate 331
Next, as shown in FIG. 8C, an ultraviolet light is radiated from the back surface side of the element disposition substrate 331 through the opening portions 333 of the mask layer 332, thereby selectively curing the ultraviolet curable resin layer 308a stuck to the elements 305 located in the element mounting positions, respectively. As a result, the elements 305a are firmly fixed to the element disposition substrate 331.
Next, as shown in FIG. 8D, the temporary holding substrate 321 and the element disposition substrate 331 are quietly separated from each other. The elements 305a located in the respective element mounting positions and firmly fixed to the temporary holding substrate 331 are left on the element disposition substrate 331 to be selectively transferred from the temporary holding substrate 321 to the element disposition substrate 331 (elements 306). On the other hand, other elements 305 to which the ultraviolet curable resin layer 308 which does not receive the radiation of the ultraviolet light radiated thereto and thus is kept uncured is stuck are separated from the element disposition substrate 331 while being held on the temporary holding substrate 321 (elements 307). The elements 307 none of which is transferred to the element disposition substrate 331 wait for the transfer in a transfer process in and after next time.
Although in this embodiment, the case where the ultraviolet curable resin layer 308 is disposed on each of the surfaces of the elements 305 is shown, the same transfer can be carried out even when the ultraviolet curable resin layer 308 is disposed on the surfaces of the element disposition substrate 331.